We intend to pursue in the coming year our study on the processing of sIgA in the mammary gland along four main lines: 1. Complete the subcellular localization of sIgA and its subunits in the mammary gland at different stages of differentiation (virgin, mid-pregnant, lactating and regressing) using both a diffusion and a surface localization procedure. 2. Analyze and characterize the kinetic and specificity of IgA transport in organ explants and dissociated cells of differentiated mammary gland. 3. Define the culture conditions for the differentiation of dissociated mammary gland cells and the onset of milk secretion with a special reference to sIgA processing. 4. Characterize conjugates formed with a heme octapeptide and different ligands (antibody, hormones, dimeric IgA) using newly synthesized bifunctional reagents.